MONTPELIER, Vt. — The 1,500 cows at Blue Spruce Farm in Bridport are producing more than just milk. They’re generating electricity.

The methane gas from their manure is being used to produce electricity for Vermont’s largest utility.

“This is the first time anywhere in the country that a farm-based generation has been offered to customers as a renewable choice,” Central Vermont Public Service Corp. spokesman Steve Costello said Friday.

Other farms have generated electricity for their own use, he said.

From gas to electricityThe manure is heated up and then produces methane gas as it breaks down. The gas is collected and used to power a generator, which sends electricity onto the power grid.

So far about 1,000 customers have signed on to pay about 4 cents more per kilowatt-hour for their electricity to support the farmers. Residential households ordinarily pay about 12 cents per kilowatt-hour.

Earl Audet, who owns the farm with his brothers, expects the cows to produce enough electricity to power roughly 330 households.

“The girls are now officially producing two streams of income, a milk check and a power check,” said Earl Audet. “This is one more way to diversify the farm, improve our bottom line, and manage our manure responsibly.”

It will take about three weeks for the manure to decompose.

Audet has said he hoped the sale of power would cover the farm’s $70,000 annual electric bill. The Audets also hope to be free of debt in seven years, Costello said.

Costs, other benefitsWhile the utility hopes other farmers will make more of their manure, getting started is not cheap. It cost the Audets about $1.2 million, half of which was covered by state and federal grants.

Generating electricity from manure has other advantages.

Extracting the gas from the manure gets rid of close to 90 percent of the smell. The cooked manure can also be used as bedding for animals and compost.